Onshore or offshore drilling rigs are used in exploration, drilling and production of hydrocarbons. The drilling rigs include a derrick or a mast with a hoisting system for lifting and lowering of pipes and other equipment into or out of the well. The hoisting system typically consists of a wire or cable, a so-called drill-line, a crown block at the top of the derrick or mast, and a traveling block both with a number of sheaves, a drawworks, a deadline anchor, and a drilling storage drum for wire or cable. The storage drum and the deadline anchor in such a hoisting system will usually be arranged on one side of a derrick or mast, while the drawworks will be arranged on the opposite side of the derrick or mast, where a wire or cable then will run from the storage drum and deadline anchor on one side of the derrick, over a number of sheaves in the derrick or mast, and onwards to the drawworks on the other side of the derrick or mast.
One challenge with such a hoisting system is that individual sections of the wire or cable will, after a period of use, be exposed to more wear than other sections. This is due to the fact that, due to reciprocating motion, the wire or cable comes into contact with the sheaves in the crown block and the traveling block along the same wire sections a large fraction of the operating time. The wear is greatest where the wire or cable rolls on and off the sheaves in the crown block and traveling block with large loads, especially at the lower position for the traveling block due to high load from the acceleration and retardation force. This wear leads to the entire wire or cable needing to be replaced after a time in use in order to avoid the risk of the system crashing or a major breakdown of the hoisting system as a result of wireline or cable breakage. An alternative to replacing the entire wire or cable is to perform a so-called “cut and slip” operation. In such an operation or procedure, a predetermined length of wire or cable is manually reeled off from the drawworks drum and stored temporarily on the drillfloor or another nearby area, and the reeled off wire or cable is cut close to the drawworks drum. The remaining length of wire or cable left on drawworks drum, is then removed for disposal. The reeled off, temporararily stored wire or cable is then reeled onto the drawworks drum, and the wire or cable can be loosened from its locking clamp on the deadline anchor so that new wire or cable is reeled off from the storage drum, over the deadline anchor and sheaves, and onto the drawworks drum with a length corresponding to the length of the wire or cable which was cut and disposed of. The deadline wire or cable is then locked onto the deadline anchor.
When the wire or cable must be replaced, which must occur after a certain number of ton-miles (ton-miles being the sum of all loads in tons and the distance hoisted or lowered in miles) to prevent fatigue and/or too high wear of the wire or cable, this is currently done manually and involves a large number of the drilling crew.
Depending on the type of operation, replacement of sections of wire or cable is done approximately on a weekly basis in order to ensure that all possible high-stress wireline sections or vulnerable points on the wire or cable are moved along the drill line wire or cable to a less exposed location. The most highly stressed locations for such fatigue or high wear are in the curve of the respective sheaves when a traveling block in the hoisting system is in one of its two end positions, i.e., when the block is close to a drill floor or near the derrick top.
The present manual operation requires that a large number of people (typically around six persons) must manually pull/tension the wire or cable during reeling off or on to thereby replace wire or cable on one or more drums of the drawworks.
A need therefore exists for an improved method and apparatus to change the wire or cable in a hoisting apparatus, in particular for “cut and slip” operations in order to reduce personnel involved in the operation and at the same time to increase safety and efficiency.